In his pioneering work on outflow shock chemistry [1]} brought the first hints of HCN abundance enhancement in protostellar shock region. At that time, only a low number of molecular transitions was observed with the IRAM 30m telescope, hence preventing an accurate determination of the excitation conditions and molecular abundances. From a theoretical point of view, both the dependence of the HCN/HNC ratio to the temperature and the sputtering of dust grains are two processes which could a priori alter molecular gas abundances of HCN and HNC across a shock.
